For many decades, half duplex two way radio networks have provided reliable and convenient communications using limited shared radio resources. For example, “walkie-talkie” and citizens band (CB) radio networks have enabled users to maintain direct communication channels with other users over extended periods of time. The push-to-talk (PTT) and “instant on” features of half duplex radio devices provide desirable modes of wireless communication for users such as truckers, construction and industrial site personnel, military personnel, taxi dispatchers, police and fire personnel and numerous others. Many modern communications systems designed for public safety still typically allocate only one logical media stream in a network, which is shared among network participants. A floor control mechanism then dictates which device in the network is permitted to send media at a given time on a given stream.
Push-to-talk over cellular (PoC) is a recent technology that enables familiar PTT and “instant on” features of conventional half duplex radios, but uses mobile communication devices operating over modern cellular telecommunications networks. Using PoC, wireless communication devices such as mobile telephones and notebook computers can therefore function as PTT half-duplex radio devices for transmitting and receiving voice and/or data. Other types of PTT models and multimedia call models (MMCMs) are also available.
Floor control in a PoC session is generally maintained by a PTT server that controls communications between two or more wireless communication devices. When a user of one of the communication devices keys a PTT button, a request for permission to speak in the PoC session is transmitted from the user's device to the PTT server using, for example, a real-time transport protocol (RTP) message. If no other users are currently speaking in the PoC session, an acceptance message is transmitted back to the user's device and the user can then speak into a microphone of the device. Using standard compression/decompression (codec) techniques, the user's voice is digitized and transmitted using discrete voice data packets, such as according to RTP and internet protocols (IP), to the PTT server. The PTT server then transmits the voice data packets to other users of the PoC session, using for example a point to multipoint communication technique.
In some circumstances a user in a PTT session may seek to hide his or her identity from other participants in the PTT session. For example, during a public chat session, it may be preferable for a user to remain anonymous so that other participants in the session do not receive details of the user's identity, such as a user address defined by a session initiation protocol (SIP) uniform resource identifier (URI). Various PTT standards therefore include binary “on/off” privacy features. Such features enable a user either to hide the user's identity details from all participants in a PTT session, or to disclose the user's identity details to all participants in a PTT session.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.